(1) Field of the Invention
The present invention relates to a method for producing lower alkyl acetates. More particularly, the invention relates to a method for continuously producing lower alkyl acetates such as isopropyl acetate and sec-butyl acetate by adding lower olefins to acetic acid in the presence of an acidic ion exchange resin catalyst. The lower alkyl acetates prepared by the method of the present invention are useful as solvents and as materials for preparing perfumes.
(2) Description of Prior Art
It is well known that, when acetic acid is allowed to react with an olefin using an acidic ion exchange resin catalyst, a corresponding alkyl acetate is obtained. For example, in the case that the olefin is propylene, isopropyl acetate is obtained through the following chemical equation: EQU CH.sub.3 COOH+CH.sub.2 .dbd.CH--CH.sub.3 .fwdarw.CH.sub.3 COOCH(CH.sub.3).sub.2
In the case that an olefin of 1-butene or 2-butene is used, sec-butyl acetate is obtained through the following chemical equations (Japanese Patent Laid-Open Publication (Kokai) Nos. 49-100016 and 55-102530): EQU CH.sub.3 COOH+CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.3 .fwdarw.CH.sub.3 COOCH(CH.sub.3)CH.sub.2 --CH.sub.3 EQU CH.sub.3 COOH+CH.sub.3 --CH.dbd.CH--CH.sub.3 .fwdarw.CH.sub.3 COOCH(CH.sub.3)CH.sub.2 --CH.sub.2 --CH.sub.3
Concerning the above esterification, liquid phase reaction, gas phase reaction and gas-liquid mixed phase reaction are known in view of the types of reaction. The gas phase reaction is not desirable in industrial practice because the polymerization of olefin on the catalyst, which disadvantageously reduces the effect and life of catalyst, cannot be avoided. Japanese Patent Publication (Kokoku) No. 59-44295 discloses gas-liquid phase reaction in which liquid phase acetic acid and gas phase propylene are cocurrently mixed. In this reaction, the catalytic efficiency can be improved because the liquid acetic acid moistens the surfaces of catalyst particles, and as a result, it is possible to carry out the reaction under moderate conditions. This can be applied to the reaction using other olefins such as linear butenes or the like.
However, because a gas phase olefin is passed through a layer of catalyst, the disadvantage that the catalytic efficiency is inevitably lowered, cannot be avoided. Furthermore, in the case of gas-liquid mixed phase reaction, the olefin dissolved in acetic acid is considered to participate in the reaction. When an olefin dissolved in a liquid phase is consumed through the reaction in esterification, the gas phase olefin must be additionally dissolved into the liquid phase, which takes a lot of time. Therefore, the liquid phase reaction in which both the acetic acid and an olefin are used in a liquid phase, is preferable in the industrial practice.
With regard to the mode of reaction in the above esterification, continuous process is more advantageous than batchwise process in view of industrial practice. In the case of continuous process, a continuous vessel-type reactor, a flow-type fixed bed reactor, a moving bed-type reactor, and a fluidized bed-type reactor are used. In view of the cost required of the apparatus and maintenance, a fixed bed continuous tubular reactor is most desirable. Nevertheless, in the reactor of this type in an industrial scale, the temperature rise inevitably occurs along the stream of reactants because the above reaction is intensely exothermic. Therefore, the rate of reverse reaction to decompose the produced alkyl acetate into acetic acid and an olefin is increased. For this reason, not only the final conversion ratio of olefin cannot be raised but also it was found out that the catalytic activity, especially the activity of ion exchange resin catalyst, is lost. Accordingly, in order to attain a high conversion ratio of olefin and a high catalytic activity, it is necessary to control properly the temperature distribution in the reaction zone.
For example, a multi-tube fixed bed reactor is disclosed in European Patent Publication No. 0 054 576 A1. When the above reaction is carried out in a gas-liquid mixed phase or liquid phase using a complicated multi-tube fixed bed reactor, it is not desirable that the cost for the reaction equipment is high because the reactor must be sufficiently resistant to pressure. In addition, the maintenance operation such as change of catalyst and so forth is quite troublesome.
Accordingly, development of an easy and inexpensive method for controlling reaction temperatures is eagerly wanted in order to carry out the above esterification using a single tube fixed bed reactor which is advantageous in view of the cost and maintenance.